Effect of rare earth elements on the microstructure and texture development in magnesium–manganese alloys during extrusion

doi:10.1016/j.msea.2010.07.081

Materials Science and Engineering: A

Volume 527, Issue 26, 15 October 2010, Pages 7092-7098

https://doi.org/10.1016/j.msea.2010.07.081 Get rights and content

Abstract

Single additions of the rare earth (RE) elements cerium, yttrium or neodymium have been made to magnesium–manganese alloys in order to investigate their influence on the microstructure and texture formed during indirect extrusion and the resulting mechanical properties. Whereas the binary Mg–Mn alloy M1 exhibits a 〈10.0〉 or 〈10.0〉–〈11.0〉 fibre texture depending on the extrusion rate, the RE-containing alloys exhibit weaker recrystallisation textures and the formation of a new texture component. The preferential growth of grains having 〈11.0〉 parallel to the extrusion direction was hindered in these alloys. For the rare earth elements used in this work it appears that Nd is a much stronger texture modifier compared to Ce or Y in Mg–Mn alloys. The weaker texture leads to increased ductility, lower yield and ultimate stresses, but a decrease in the asymmetric yield behaviour of the extruded bars.

Research highlights

▶ A new texture component is developed during extrusion of Mg–Mn alloys. ▶ Nd is a much stronger texture modifier compared to Ce or Y in Mg–Mn alloys. ▶ Recrystallisation is impeded in RE-containing Mg–Mn alloys. ▶ The weaker texture leads to increased ductility and decreased yield asymmetry.

Introduction

Extrusion plays an important role in extending the technical applications of wrought magnesium alloys. The broader use of such alloys and their semi-finished products is, however, restricted by their limited ductility and mechanical anisotropy at ambient temperatures [1]. These limitations result from the low symmetry of the hcp lattice structure of magnesium and its alloys which reduces the number of active slip systems. A further consequence of this is that strong textures develop during thermo-mechanical processing of magnesium alloys. Such textures result from preferred re-orientation due to the dominant deformation mechanisms such as basal slip and twinning. Furthermore, dynamic (DRX) or subsequent static (SRX) recrystallisation influences the texture development if processing is carried out at elevated temperatures [2]. During the extrusion of round bars, typically, a prismatic 〈10.0〉 fibre texture develops which may migrate to a 〈10.0〉–〈11.0〉 double fibre texture. This texture aligns the basal planes strongly into the extrusion direction [3], [4]. These preferentially developed grain orientations are unfavourable for basal slip, which is the most easily activated deformation mechanism and thus limit the ductility if tensile testing is carried out on samples oriented parallel to the extrusion direction.

It has recently been shown that sheets [5], [6], [7], [8] and extrusions [9], [10], [11] with weaker textures or broader orientation distributions of the basal planes have increased ductilities. The alloys used in these studies all contained a certain amount of a RE or a mixture which is usually based on cerium or neodymium (misch metal). Magnesium alloys containing Mn and single RE elements tend to form weak textures after extrusion. Profiles with such weak textures give rise to higher ductility as well as a small or vanishing asymmetry in tensile and compressive yield strength [12]. This present study aims to investigate the origin of such textures formed during extrusion and to analyse the recrystallisation behaviour. For this purpose, the microstructures and textures of extruded Mg–Mn based alloys containing single RE elements were examined using the XRD and EBSD techniques.

Section snippets

Experimental

In Table 1 the alloy compositions including the pure element additions of cerium (E), yttrium (W) and neodymium (N) are given. Alloy names follow ASTM procedures using the above letters for each element. All alloys were gravity cast to produce billets for extrusion which were machined to a diameter of 93 mm. The billets were homogenised at 350 °C for 15 h prior to extrusion. Indirect extrusion was carried out at 300 °C to produce round bars with a diameter of 17 mm, which corresponds to an extrusion

Microstructure

Micrographs from longitudinal sections of the extruded profiles are shown in Fig. 1. After slow extrusion, alloy M1 (Fig. 1a) exhibits a partially recrystallised microstructure which consists of large, elongated, unrecrystallised “grains” surrounded by newly formed, recrystallised grains [3]. After fast extrusion, the alloy shows a fully recrystallised microstructure and a significantly larger recrystallised grain size (average 70 μm) compared to slow extrusion (average 8 μm). The same basic

Microstructure and texture development

The results shown in Fig. 4, Fig. 5 have to be considered in the context of mechanisms that determine the development of microstructure and texture during processing. These are namely texture changes due to the active deformation mechanisms such as slip and twinning on the one hand, and in addition, changes that result from the nucleation and growth of new grains during DRX and SRX. The first aspect depends on the balance of the various deformation mechanisms by which the deformation texture is

Summary and conclusions

In summary, it was found that recrystallisation is impeded in RE-containing Mg–Mn alloys compared to alloy M1, which results in smaller grain sizes. This allows a new texture component to be developed during extrusion which implies changes in both the deformation and the recrystallisation mechanisms.

The texture of the profile is understood as a result of different competing mechanisms which lead to changes in the recrystallisation kinetics. It is likely that boundary pinning caused by the RE

Acknowledgements

The authors would like to thank Dr. P. A. Beaven at GKSS Research Centre for intensive discussions and Dr.-Ing. Sören Müller for his help with the extrusion experiments at the Extrusion Research Centre of the University of Technology in Berlin (Germany).

References (24)

J. Bohlen et al.
Scripta Mater.
(2005)
J. Bohlen et al.
Acta Mater.
(2007)
C.E. Dreyer et al.
J. Mater. Process. Technol.
(2010)
E.A. Ball et al.
Scripta Metall. Mater.
(1994)
N. Stanford et al.
Scripta Mater.
(2008)
B.H. Lee et al.
J. Mater. Process. Technol.
(2007)
N. Stanford et al.
Scripta Mater.
(2008)
N. Stanford et al.
Mater. Sci. Eng. A
(2008)
K. Hantzsche et al.
Scripta Mater.
(2010)
S.R. Agnew et al.
Acta Mater.
(2001)

R. Cottam et al.

Mater. Sci. Eng. A

(2008)

J.D. Robson et al.

Acta Mater.

(2009)

Cited by (351)

Insights into heterogeneous nucleation interface of Y<inf>2</inf>O<inf>3</inf>//NbN via first principles calculation
2024, Materials Today Communications
The heterogeneous nucleation interface between Y₂O₃ and NbN was investigated by first principles method in this paper. The different low index interfaces mismatch degrees of Y₂O₃//NbN were calculated. Then, the interface models of Y₂O₃//NbN were constructed, and their interface properties were analyzed. The results show that the mismatch degree of Y₂O₃(111)//NbN(110) interface is the smallest, which is 7.61%. It reveals the effectiveness of Y₂O₃ as the heterogeneous nucleation nucleus of NbN is medium. Four interface models of Y₂O₃(111)//NbN(110) interface are constructed, namely Y-NbNⅠ, Y-NbNII, O-NbNⅠ and O-NbNII interfaces. Among them, the adhesive work of O-NbNII interface is the largest, which is 6.26 J/m², and its interface energy is the smallest, which is −3.08 J/m². The O-NbNII interface mainly involves the binding of Nb-O ionic bonds, and N-O covalent bonds. Therefore, Y₂O₃ can serve as the heterogeneous nucleation nucleus of NbN, and the O-NbNII interface is the most stable one.
Hot deformation behavior and extrusion temperature-dependent microstructure, texture and mechanical properties of Mg–1Mn alloy
2024, Journal of Materials Research and Technology
Mg–1Mn alloy, extruded at a low temperature in our published protocol, contributed to the intensified basal texture and extremely refined microstructure with spheroidal nanoscale precipitates dispersing throughout the matrix and along the grain boundaries, consequently resulting in the excellent mechanical properties where the alloy exhibited a tensile yield strength of 204.3 MPa and a ductility of 38.8% at room temperature. Therefore, Mg–1Mn alloy was recommended as one of the potential materials for structural applications. In the present investigation, hot deformation behavior through constitutive analysis and extrusion temperature-dependent microstructure, texture and mechanical properties of as-extruded Mg–1Mn alloy were investigated, aiming at revealing how extrusion temperature affected microstructure, texture, and mechanical properties of as-extruded Mg–1Mn alloy. X-ray diffraction patterns demonstrated that phase components of the experimental alloys consisted of the α-Mg matrix and Mn precipitates. Optical microscopy images indicated a significant increase in average grain size of the alloys as the extrusion temperature increasing from 250 °C to 400 °C. Scanning electron microscopy graphics revealed that coarsened particles identified as Mn precipitates by EDS were observed within the matrix when extrusion temperature reached 400 °C. Inverse pole figure maps of the experimental samples subjected to different extrusion temperatures in the present work exhibited the typical basal texture, suggesting that basal slip was activated hardly during the tensile stress applied along the extrusion direction. Consequently, extrusion temperature displayed the significant impact on microstructure, texture, and mechanical properties of as-extruded Mg–1Mn alloy. The alloy extruded at both 250 °C and 300 °C exhibited the strong basal texture and refined microstructure with spheroidal nanoscale precipitates dispersing within the matrix and along the grain boundaries, which contributed to their excellent comprehensive mechanical properties. The alloy extruded at 400 °C possessed the typical basal texture and coarsened microstructure, leading to the extremely poor mechanical properties. Simultaneously, the constitutive model of the Arrhenius equation based on Zener-Hollomon parameters was also established in the present investigation. Therefore, optimizing the extrusion temperature to regulate the microstructure, grain orientation distribution, and morphology of precipitates was considered as one of the effective approaches for achieving the excellent mechanical properties of Mg alloys.
Effect of pre-twinning and heat treatment on formability of AZX311 Mg alloy
2024, Journal of Magnesium and Alloys
In this study, the effects of pre-strain-induced tensile twins (TTWs) and controlled heat treatment on the formability behavior of AZX311 Mg alloy sheets were investigated. A 4% compressive strain was applied to pre-strain the sheets using the in-plane compression (IPC) technique along the rolling direction (RD) to introduce TTWs. The pre-strained (PS) samples were subsequently heat-treated at 250 °C, 350 °C, and 400 °C independently for 1 hr, and are termed as PSA1, PSA2, and PSA3, respectively. Erichsen cupping tests were conducted to assess the formability of the sheet samples under different initial conditions. The results showed that the PS sample heat-treated at 250 °C for 1hr exhibited a decrease in the Erichsen index (IE) compared to the as-rolled sample, whereas PSA2 and PSA3 samples showed an increase in IE values. Microtexture analysis revealed that most of the TTWs generated through pre-twinning were stable at 250 °C; however, the twin volume fraction reduced to 41% at 350 °C compared to the PS samples due to enhanced thermal activity at that temperature. Furthermore, PSA2 samples showed severe grain coarsening in some areas of the sample, and the fraction of such grains increased in the PSA3 samples. The stretch formability (IE value) of PSA2 samples showed a 32.3% increase compared to the as-rolled specimens. Additionally, the analysis of the deformed specimen at failure under the Erichsen test indicated that considerable detwinning occurs in the PS and PSA1 samples, whereas dislocation slip activity dominates in the PSA2 and PSA3 samples during stretch forming. Apart from detwinning and dislocation slip, deformation twins were also observed in all samples after the Erichsen test. Thus, this work highlights the importance of texture control and its underlying mechanisms via pre-twinning followed by heat treatment and their impact on the room temperature (RT) stretch formability of AZX311 Mg alloy sheets.
A visco-plastic self-consistent analysis of the compression anisotropy in extruded rare earth magnesium alloy
2024, Journal of Materials Research and Technology
The anisotropy of rare earth magnesium (Mg-RE) alloys has attracted significant attention. In this study, the room-temperature compression anisotropy of the extruded Mg-8.5Gd-4.5Y-0.8Zn-0.4Zr alloy was investigated utilizing techniques such as optical microscope (OM), electron backscatter diffraction (EBSD), and viscoplastic self-consistent (VPSC) modeling. The results show that the C0 (with the axis parallel to the extrusion direction) sample exhibited the greatest yield strength of 290 MPa, while the C45 (with the axis inclined at a 45° angle to the extrusion direction) and C90 (with the axis perpendicular to the extrusion direction) samples had yield strengths of 223 MPa and 250 MPa, respectively. The VPSC hardening parameters were significantly adjusted in this study based on the Schmid factor of deformation modes in Mg-RE alloy, particularly increasing the τ₀ (Critical Resolved Shear Stress, CRSS) for basal<a> slip. The ratios of CRSS for other deformation modes to basal<a> slip were approximately as follows: CRSS_Twin/CRSS_Bas = 2, CRSS_Pri/CRSS_Bas = 2.7 and CRSS_Pyr/CRSS_Bas = 3.3, while these ratios in non-rare earth magnesium alloys typically ranged between 0.8 and 3, 5–10 and 8–20. The stress-strain curves and pole figures obtained from the VPSC model exhibited a good agreement with experimental results. Based on the VPSC simulation results, the disparity in the activation level of basal<a> slip was identified as the primary cause of mechanical anisotropy. Twinning only played a significant role in the early phases of deformation, which was not the most primary factor on yield anisotropy.
Investigating effects of element composition on the microstructure and mechanical properties of three types FeCrAl alloys through small punch test
2024, Materials and Design
This study investigated the effects of element composition on the microstructure and mechanical properties of three FeCrAl alloys (denoted as Q1, Q2, Q3). The addition of reactive elements (REs) 2 wt% Mo resulted in a 60 % refinement of grain size and an increase in kernel angle misorientation (KAM). Alloy texture was notably influenced by elemental composition, and γ texture (1 1 1)[0 $\bar{1}$ 1] exhibited higher energy than (1 1 1)[1 $\bar{2}$ 1]. The {1 1 0} 〈1 1 1〉 slip system exhibited greater resistance to deformation and lower susceptibility to activation than {1 2 3} 〈1 1 1〉. The yield load ( $P_{y - C E N}$ ), maximum load ( $F_{m}$ ), and fracture energy ( $E_{sp}$ ) of the alloys at 298 K, 573 K, 723 K, 873 K, and 1023 K were evaluated through small punch test (SPT). The $F_{m}$ of the three alloys were two-staged with notable temperature dependence. In this context, Q1 exhibited the lowest absolute slope of 2.97 (Q2: 3.44, Q3: 3.46) in the second stage. Furthermore, the $E_{sp}$ value of Q3 was the lowest at room temperature (RT, 298 K) and the highest at high temperatures (873 K and 1023 K) among the three alloys. The obtained results of SPT at different temperatures suggested a strong temperature dependence in the mechanical properties.
CALPHAD-guided design of Mg-Y-Al alloy with improved strength and ductility via regulating the LPSO phase
2024, Acta Materialia
This work performed a CALPHAD-guided design strategy to develop high strength-ductility Mg–Y–Al alloy by taking advantage of the strengthening effect of the LPSO phase and the ductilizing effect of the α-Mg matrix. To achieve this goal, the LPSO phase content and the Y content in the α-Mg matrix were quantitatively optimized via calculations of the isoplethal section and phase fraction diagrams. Based on this, three typical Mg-Y-Al alloys without the LPSO phase and with varying LPSO contents were designed. The strength of the alloys was significantly improved by the introduction of the LPSO phase and the increase in its content. However, the ductility of the alloy was maintained while increasing the LPSO content. Through analyzing the strengthening and ductilization mechanisms, it was revealed that the LPSO phase can strengthen the extruded alloys by refining the dynamic recrystallized grain size, exerting a short-fiber-like strengthening effect, and dislocations strengthening effect by hindering <c+a> dislocations movements. The ductile α-Mg phase with considerable Y content can effectively withstand plastic strain by operating multiple slips during the deformation, significantly improving the ductility of the material. The results of this study inspired the development of an effective design strategy to produce high strength-ductility Mg-Y-Al alloys by quantitatively optimizing the LPSO phase and Y contents in the α-Mg matrix, as well as to design high-performance Mg alloys for engineering demands in the future.

View all citing articles on Scopus

View full text

Effect of rare earth elements on the microstructure and texture development in magnesium–manganese alloys during extrusion

Abstract

Research highlights

Introduction

Section snippets

Experimental

Microstructure

Microstructure and texture development

Summary and conclusions

Acknowledgements

Scripta Mater.

Acta Mater.

J. Mater. Process. Technol.

Scripta Metall. Mater.

Scripta Mater.

J. Mater. Process. Technol.

Scripta Mater.

Mater. Sci. Eng. A

Scripta Mater.

Acta Mater.

Mater. Sci. Eng. A

Acta Mater.